Everyone says beeswax, but I don't get it. I mean I've got it and have used it, but what does it do? It's crumbly and falls out right away. It doesn't seem to make the zipper open and close any easier, not that I can tell anyway.
When a zipper wears out, the rubber part starts to frey. After some time, the freying gets to the teeth and it starts to leak, or it pulls apart. I don't think the metal wears out so much as the soft rubber deteriorates.
The beeswax only gets on the outside of the metal and between the teeth. Wax is kinda stiff, so it falls out in little chunks, or stays wedged in the zipper where it can hold foreign matter. Then to clean it out you need to brush across the teeth, which I would think is hard on the rubber.
Beeswax also gets brittle when cold, although it is waterproof.
Superior Diving sent me some liquid stuff that had the texture of tapioca. Once applied, the zipper opened and closed as easy as the zipper on my winter coat and cleaned up easily.
Wouldn't a good zipper product have those qualities, as well as some kind of rubber conditioner/protector like Seal Saver?